[Mgs] MGB driving me nuts

Paul Hunt paul.hunt1 at blueyonder.co.uk
Fri Sep 5 02:18:30 MDT 2008


Several oddities here.  If the fuel in the tank was expanding, causing a
'whoosh' when you removed the filler cap and spurting out of the filler hole,
then the vent was blocked which would mean that fuel from the tank couldn't
flood the carbs.  The tank should have a limiting chamber that is designed to
prevent fuel leaking from the filler on expansion, unless its bleed vent were
blocked or a non-limited tank was installed.  If the vent were not blocked,
then expansion would run into the canister and from there onto the ground.  It
couldn't get to the carbs unless there were other blockages in the canister
plumbing.  If the outlet to the canister were blocked, but the tank vent were
not, then there is a possibility of *air* pressure from the tank going into
carb vents, which would push the fuel level down in the float bowl and
consequently up out of the jet, so flooding the engine, possibly emptying the
float bowls.  The carbs may flood themselves if the float level is too high,
simply from expansion of the fuel in the float chamber and nothing else.  But
that has never happened on my V8, when switching off on very hot days I can
hear the fuel boiling in the float bowls and see fumes pouring out of the
vent, but no fuel dripping out and no flooding.  When I do restart some time
after that the fuel pump chatters away like mad for several seconds as it is
having to refill both float bowls.

PaulH.
  ----- Original Message -----
  ...   But then I learned that if you fill the tank and the car is parked on
  hot tarmac for a couple of hours with a blocked vent line, the fuel
  expands enough to flood the carbs and to blow out of the filler cap when
  the cap is removed.
  ...
     The whoosh of air was the key to the problem. I had not noticed the
  slight vacuum/suction on short drives before the exciting event.


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